Looks like they've been extremely profligate in allocating half the HDD to the D: partition - but is there anything in the documentation to suggest that you shouldn't use the space in it for your own data?.

As to removing those 2 partitions, you'll need a little more information about how they are used - I know that Dell have similar partitions (but better space allocation), and warn that any change to the disk organisation can stop the 'automatic' recovery process (which restores the HDD to the state in which they left it). I can verify that this statement is true, and recently spent quite a while trying to recover a usable OS when a HDD failed. If you have the resources, I recommend a full disk image be taken before you do anything more.

Thx. Shrinking C: and D: doesn't look like an insurmountable task though it'll involve some fiddling with 'unmovable' files. Thing is, I think I already have 3 primary partitions. Shrinking both would leave me with hundreds of GB's of worthless disk space unless there's a way to move C: and D: into the same corner of the HDD.

Would it be a better idea to just wipe the HDD and reinstall Windows from the recovery disks?

Indeed... Just found that out myself: no choice about the partition table. Already deleted the D: and shrunk the new C:
Installed PerfectDisk in order to delete the 'nameless' Q:
Will spend tomorrow reinstalling and tweaking and fiddling but I guess there's valuable lesson in there somewhere...
(o:

Don't know what I was thinking installing a defragmentation tool to delete a partition... Thought I'd seen a button somewhere though. Guess I'll have to do my deleting some other way.
That is if it makes sense cause I noticed something annoying: the 'nameless' 400MB Q: is on sda1. If I delete it, can I turn sda2 (C:) into my new sda1 and go from there or am I stuck with the 400MB?

I thought I had already posted this update (apparently not) but in case anyone is still interested: deleting the nameless Q: was definitely not a good idea. Turns out it is the windows boot partition so I ended up with the proverbial paperweight. My hope that I could then repartition to my own liking when I had to reinstall windows was also in vain: the reinstall automatically uses the same setup.

So eventually I left Q: alone, used PerfectDisc to shrink C: to 100Gb, put /boot on the 3rd primary partition and everything else (/, swap, /home and D:) on an extended 4th of 600Gb. This works... so far.